U.S. Pat. No. 6,199,532 discloses an internal combustion engine wherein a flow connection is provided between the inlet channel and the crankcase. It has been shown that the flow connection has a large influence on the charge cycle in the combustion chamber. Especially during idle, the running performance of the engine is so affected that the idle stability of the engine is reduced.
It has furthermore been shown that a better engine acoustic is achieved during idle in separately lubricated engines than in mixture-lubricated engines.